Air-Brake Auxiliary Components

The Brake System:

Auxiliary Components

Some wheeled vehicles require special controls on the braking system.

If we consider a 4x4 truck tractor, for example, we know that its primary job is to pull a semitrailer. Under normal driving conditions when the road is dry, the braking system will work well. When the road is wet and slippery, though, the tractor and trailer will jackknife if the front wheels of the tractor brake too much. To prevent this from happening, the front quick-release valve contains a limiting valve. A two-way valve is also provided to control the limiting valve.

The two-way valve is mounted in the vehicle cab where the operator can reach it easily. The valve has dry and slippery road positions.

An air line connects the valve to the brake valve and another line goes from the two-way valve to the combined limiting and quick-release valve at the front axle.

When the valve is in the dry road position, no air can pass through the two-way valve to the front axle. However, when the valve is in the slippery road position, air from the brake valve passes through the two-way valve and onto the quick-release valve. When this air acts on the limiting device in the quick-release valve, it only allows a small amount of air coming from the brake valve to go to the brake chambers. This will reduce the amount of braking action on the front wheels and prevent the front brakes from locking which would cause the tractor and trailer to jackknife.

Trucks and truck tractors that pull heavy trailer loads must also have a control that will allow the operator to apply the trailer brakes separately from the truck or tractor brakes. This device is known as an independent trailer control valve and is usually mounted on the truck steering column. Notice in the paragraph above that the valve is connected to reservoir air pressure through the manifold fitting for auxiliary devices.

The hand lever on the valve allows the operator to apply line air pressure to the double-check valve at the rear of the vehicle. This valve allows pressure to be applied on the trailer brakes through the trailer service line connection.

Notice that the double-check valve also has a line coming to it from the brake valve. In this way, the trailer brakes can be operated when the truck brakes are applied or they can be applied alone with the use of the trailer control in the cab.

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Article Pages
1. The Brake System
2. Introduction
3. Principles Of Braking
4. Braking Requirements
5. Factors Controlling Retardation
6. External-Contracting And Internal-Expanding Brakes
7. Brake Types
8. Brake Drum Construction
9. Brake Shoes
10. Rotating And Non-Rotating Units
11. Self-Energizing Action
12. Disc Brake
13. Comparing Disc And Drum Brakes
14. Floating Caliper
15. Fixed Caliper
16. Hydraulic Brakes
17. Master Cylinder
18. Wheel Cylinder
19. Hydraulic Brake System Insepction
20. Before Road Test Inspection
21. Road Test Inspection
22. After Road Test Inspection
23. Air-Hydraulic Brake System
24. Air-Hydraulic Master Cylinder
25. Air-Hydraulic Cylinder
26. Air Compressor
27. Air Governor
28. Air-Hydraulic Brake System Components
29. Trailer Coupling Hoses And Connectors
30. Air-Over Hydraulic Cylinder
31. Operation Of Air-Hydraulic Brakes
32. Air-Hydraulic Brakes Of Large Trucks
33. Trailer Air-Over-Hydraulic Brake Systems
34. Air-Hydraulic Brake System Inspection
35. Before Road Test Inspection
36. Air-Hydraulic Brake System Road Inspection
37. Trouble Shooting Air-Hydraulic Brakes
38. Air-Brake System
39. Air-Brake Quick Release Valve
40. Air-Brake Relay Valve
41. Air-Brake Chamber
42. Air-Brake Slack Adjuster
43. Air-Brake Auxiliary Components
44. Semi-Trailer Air Brake Systems
45. Operation Of Straight Air-Brake System
46. Miscellaneous Air-Brake Components
47. Troubleshooting Straight Air Brake Systems

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